Repeater system for use on a moveable object

ABSTRACT

A repeater system includes a first master unit and a second master unit located on the movable object, such as a train. The master units are each connected to an antenna for receiving a downlink RF signal from at least one base station outside of the movable object and for transmitting an uplink RF signal towards the base station. Remote units are associated with different coverage areas within the movable object and are connected to the master units unit via a transport medium. The remote units are each connected to an antenna system for transmitting the downlink RF signal into the associated coverage area of the movable object and for receiving the uplink RF signal from the coverage area. A control unit can control first gain for the connection with the first master unit and a second gain for the connection with the second master unit.

CROSS-REFERENCE TO RELATED APPLICATION

This claims priority to European Patent Application number EP15161405.4,titled “Repeater system for use on a movable object” and filed Mar. 27,2015, the entirety of which is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to telecommunications systems.More specifically, but not by way of limitation, this disclosure relatesto a repeater system for use on a movable object and to a method forcontrolling a repeater system.

BACKGROUND

Repeater systems can serve a wide frequency band, for example a complete3GPP band. A frequency band typically contains multiple carrierscarrying information according to different communication technologiesand standards such as GSM, UMTS, LTE or the like.

A repeater system of this kind may for example be used on a train toprovide network coverage within the train.

High-speed train applications in this regard can present challenging RFenvironments. The complexities of different terrain combined withrapidly changing outdoor signal levels of the various networks can makeit difficult for operators to provide the coverage and service theircustomers demand while travelling from city to city or to anothercountry. To improve the reliability of wireless signals on trains,repeater systems in the shape of so-called distributed antenna systems(DAS) have proven to be cost-effective. A DAS may for example beinstalled within a train and serve to amplify a signal to compensate anattenuation caused by the train (due to, for example, metalized windowson high-speed trains reducing signal penetration into the traincarriages, which may result in spotty coverage and dropped calls).

A DAS generally may be installed within a train and amplify, duringoperation, a signal between a pick-up antenna at the outside of thetrain and an antenna network within the carriages of the train. On theone hand, the DAS compensates the attenuation of the signals caused bythe train. On the other hand, however, the signals of all users arecombined and communicated via a single (or a few) common pick-up antennamounted on the outside of the train. In case the train enters acommunication cell of another base station, this can inherently cause asimultaneous handover (HO) of multiple users located inside the trainand communicating via the repeater system. Thus, a large number ofhandovers of the multiple users located within the train may occur in avery short timeslot, which may, depending on the train speed and theoverlapping area of the base stations taking part in the handover,increase the so-called handover outage probability.

One solution to alleviate this problem is to use several independentrepeater systems with several pick-up antennas. For example, eachcarriage may be equipped with an individual repeater system. Thereby,the handover scenario of the users located on the train is split bycarriage and hence into several portions as the carriages enter ahandover region with overlapping cells of adjacent base stations oneafter the other in a time-offset manner.

For example, if a distance of 50 m is assumed between the pick-upantennas of repeater systems of adjacent carriages, the handover ofusers of adjacent carriages can be triggered with a time offset of 0.51seconds, assuming the train is travelling at 350 km/h. This timedifference generally may be sufficient when considering that an expectedaverage handover time is less than 300 ms (as specified for example fora 3GPP network).

This multi-antenna concept can perform well, but has the drawback thateach carriage is equipped with a separate pick-up antenna (respectivelya separate DAS), which generally is costly. In addition, the delaybetween the handovers of the individual carriages is determined by thedistance of pick-up antennas of successive carriages and the trainspeed. Thus, in case the handover of users in one carriage fails, therepossibly is an increased interference during the handover procedures ofthe next carriage in that the mobile devices (UE) may try to re-connectto the (former) base station. This may increase the probability ofhandover outage for the following carriages.

SUMMARY

In one example, a repeater system includes a first master unit, a secondmaster unit, and remote units. The first master unit is positionable ata first location on a movable object. The second master unit ispositionable at a second location on the movable object. The firstmaster unit and the second master unit are configured to communicativelycouple to antennas for receiving, in a downlink direction, a downlink RFsignal from at least one base station external to the movable object andfor transmitting, in an uplink direction, an uplink RF signal towardsthe at least one base station. The remote units are configured to couplethrough a transport medium to the first master unit by a firstconnection and to the second master unit by a second connection. Theremote units are positionable on the movable object and associated withdifferent coverage areas within the movable object. The remote units areconfigured to couple to antenna systems for transmitting, in thedownlink direction, the downlink RF signal into associated coverageareas of the movable object and for receiving, in the uplink direction,the uplink RF signal from the coverage areas. For at least a subgroup ofthe remote units, a first gain for the first connection and a secondgain for the second connection are controllable by a control unit.

In another example, a method is provided that includes:

receiving, by a first master unit at a first location on a movableobject and a second master unit located at a second location on themovable object, a downlink RF signal in a downlink direction from atleast one base station that is located outside of the movable object;

transmitting, by remote units associated with different coverage areaswithin the movable object and connected to the first master unit and thesecond master unit via a transport medium, the downlink RF signal in thedownlink direction into an associated coverage area of the movableobject;

receiving, by the remote units, an uplink RF signal in an uplinkdirection from a coverage area;

transmitting, by the first master unit and the second master unit, theuplink RF signal in the uplink direction towards the at least one basestation; and

controlling, for at least a subgroup of the remote units by a controlunit, a first gain for a connection with the first master unit and asecond gain for the connection with the second master unit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic overview of a repeater system on a train, whichincludes a master unit connected to multiple remote units according tosome aspects.

FIG. 2 shows a schematic drawing of functional processing blocks in themaster unit and a remote unit for digital processing of an RF signal ina downlink direction according to some aspects.

FIG. 3 shows a diagram of a reference signal receive power (RSRP) of twobase stations in a handover scenario according to some aspects.

FIG. 4 shows a schematic view of a setup of different independentrepeater systems on different carriages of a train according to someaspects.

FIG. 5 shows a schematic view of a setup of a repeater system on atrain, which includes two master units and multiple remote unitsaccording to some aspects.

FIG. 6 shows a flow chart of a method for controlling gain settings ofthe repeater system of FIG. 5 according to some aspects.

DETAILED DESCRIPTION

Certain aspects and features relate to a repeater system that caninfluence the timing of handovers of mobile devices communicating viathe repeater system.

In some aspects, a repeater system for use on a movable object, forexample a train, includes a first master unit to be located at a firstlocation on the movable object and a second master unit to be located ata second location on the movable object. The first master unit and thesecond master unit are each connected to an antenna for receiving, in adownlink direction, a downlink RF signal from at least one base stationoutside of the movable object and for transmitting, in an uplinkdirection, an uplink RF signal towards the at least one base station.

Multiple remote units can be associated with different coverage areaswithin the movable object and can be connected to the first master unitand the second master unit via a transport medium. The remote units caneach be connected to an antenna system for transmitting, in the downlinkdirection, the downlink RF signal into the associated coverage area ofthe movable object and for receiving, in the uplink direction, theuplink RF signal from the coverage area.

A control unit is configured to control, for at least a subgroup of theremote units, a first gain for the connection with the first master unitand a second gain for the connection with the second master unit.

The repeater system may be used on a train. For example, the firstmaster unit may be located at the front of the train, such as on a frontcarriage of the train. The second master unit may be installed on therear of the train, such as on a rear carriage of the train (referring tothe direction of travel of the train).

In some examples, the first master unit and the second master unit areprovided on the movable object—the train in this example. The masterunits can provide a connection with one or more outside base stationsand for receiving RF signals from the outside base stations andtransmitting RF signal towards the outside base stations. On the movableobject, for example in carriages of a train, multiple remote units areinstalled. Each remote unit can be communicatively coupled to both thefirst master unit and the second master unit via a transport medium, forexample an air interface, an optical fiber connection, one or morecoaxial cables, or the like. The coupling may be a bus connection, forexample a ring bus connection or the like.

Coupling of each remote unit with the two master units can be controlledby a control unit. The control unit can be configured to control a gainof the coupling with the first master unit and the second master unit.Each remote unit can receive signals from the two master units in aweighted fashion, with the gain setting constituting weighting factors.

By gain setting of the couplings with the first master unit and with thesecond master unit, the control unit may prioritize whether a mobiledevice in the range of a particular remote unit communicates with anoutside base station via the first master unit, via the second masterunit, or via both master units.

This set-up may be useful to control handovers of mobile devices(generally denoted as user equipment or “UE”) located within thedifferent coverage areas of the movable object, for example located indifferent carriages of a train. By setting the gain, a mobile device inthe range of the remote unit can communicate with an outside basestation via the first master unit, the second master unit or both, andthe mobile device may trigger a handover in certain circumstances. Forexample, a handover may be triggered when the first master unit entersinto a handover region in between two base stations (if the mobiledevice communicates via the first master unit). A handover may betriggered when the second master unit enters into a handover regionbetween two base stations (if the mobile device communicates via thesecond master unit). A handover may be triggered if the first masterunit is in the range of a first base station and the second master unitis in the range of a second base station and if a handover criteria isfulfilled—for example if a signal received from the first base stationdrops below a certain level and a signal received from the second basestation rises above a certain level (in this case the mobile devicecommunicates via both master units, where the connections with themaster units are weighted by the gain setting of each connection and thetiming of the handover may be influenced by the gain setting).

By controlling the gain setting of the connections of the remote unitswith the master units, a handover criteria can be fulfilled at differenttimes or mobile devices communicating with different remote units withinthe movable object, for example within a train, such that the mobiledevices can enter into a handover procedure in a time-offset manner.Mobile devices on a movable object may not all at the same time start ahandover procedure, but the mobile devices can initiate a handover in atime-offset manner, thus reducing the handover outage probability.

This can be achieved with limited equipment, at least compared to asetup in which a separate repeater system is used on each carriage.Namely, only two master units need to be installed on a movable object,where the two master units are installed at displaced locations, forexample at the very front and at the very rear of a train. Each masterunit can be connected to all remote units, where the gain of theconnections can be set by the control unit.

The control unit may be configured to increase or decrease the firstgain for the connection with the first master unit or the second gainfor the connection with the second master unit. The control unit may beconfigured to dynamically change the gain settings for the differentconnections with the different remote units, depending for example onchanging environmental conditions.

In some examples, the control unit may be configured to increase thefirst gain upon decreasing the second gain and to decrease the firstgain upon increasing the second gain. The adjustment of the first gainof the connection of a remote unit with the first master unit and of thesecond gain of the connection of a remote unit with the second masterunit can occur in a concerted fashion such that the first gain isincreased when the second gain is decreased and vice versa. By adjustingthe gains in this way, the connections can be prioritized such that amobile device connected with a remote unit, according to its gainsettings, predominantly exchanges signals via the first master unit orthe second master unit.

The first gain and the second gain may be individually adjustable foreach remote unit. For each remote unit a different gain setting for thetwo connections (with the first master unit on the one hand and thesecond master unit on the other hand) may apply.

To control a handover of mobile devices in coverage areas of differentremote units, the gain settings of the different remote units can bedynamically adjusted in a concerted fashion. Namely, the first gain andthe second gain of remote units associated with neighbouring coverageareas, for example of neighbouring carriages of a train, can be adjustedconsecutively, i.e., one after the other, such that one remote unitafter the other may be switched from one master unit to the other masterunit to force a handover of mobile devices connected with the remoteunits.

The control unit may be configured to control the first gain and thesecond gain of a remote unit to force a handover of a mobile deviceconnected with the remote unit (e.g., operating in the coverage areaassociated with the particular remote unit). The mobile device may beforced to handover from a first base station spanning a firstcommunication cell to a second base station spanning a secondcommunication cell, where at least one of the first master unit and thesecond master unit is located in the range of each communication cell.For example, if the first master unit is located in the cell of thesecond base station and the second master unit is located in the cell ofthe first base station (as the train moves), by adjusting the gain ofthe connections of the remote unit such that the mobile device connectedwith the remote unit is forced to communicate via the first master unit,the mobile device is forced to handover from the first base station tothe second base station in order to keep up the connection. Although theactual handover procedure can be fully carried out between the mobiledevice and the base stations that the mobile device is communicatingwith (via the repeater system), the timing of the handover can be forcedby the settings of the repeater system.

Controlling of the repeater system may occur in different ways and basedon different criteria. For example, the control unit may be configuredto control the first gain and the second gain depending on a signalstrength measurement of a signal received from a base station. Bymeasuring the received signal strength of a reference signal obtainedfrom base stations outside of the movable object, it can be determinedif the first master unit or the second master unit are in the range ofone or multiple base stations and whether a handover may be indicatedfor mobile devices within the movable object. Alternatively, controllingmay also occur based on location information received from a positioningsystem, such as a GPS system, making use of a prior knowledge wherecells of base stations are located. If the location informationindicates that a (known) cell of a base station has been entered,controlling the gains of the connections of the remote units may beadjusted accordingly in order to force a handover of mobile devicesconnected with the remote units.

FIG. 1 shows, in a schematic drawing, a repeater system 1 that is adistributed antenna system (DAS) including a master unit 10 and multipleremote units 11. The master unit 10 may, for example, be located at acentral location on a train 4 and may include an antenna 100 by whichthe master unit 10 wirelessly connects to one or more base stations3A-3B of one or more communication networks using an air interface. Theremote units 11 are located within different carriages 40 of the train 4and serve to provide coverage throughout the different carriages 40 ofthe train 4.

The remote units 11 are connected to the master unit 10 via a transportmedium 12, for example a network of optical fibers, and can be incommunication connection with the master unit 10. Each remote unit 11includes an antenna 110 by which the remote unit 11 can connect to amobile device 5 of a user in a carriage 40 of the train 4.

In a downlink direction D, an RF input signal RF_(IN) can be receivedvia the antenna 100 at the master unit 10, processed within the masterunit 10 for transporting it via the transport medium 12 to the differentremote units 11 and, after further processing, transmitted via theantennas 110 as an RF output signal RF_(OUT). The RF output signalRF_(OUT) may be received by a mobile device 5 in a carriage 40 of thetrain 4.

Vice versa, in an uplink direction U an RF signal received at theantenna 110 of a remote unit 11 can be provided via the transport medium12 to the master unit 10 and retransmitted via the antenna 100 towardsan antenna 30 of a base station 3A of an outside communication network.

The repeater system 1 may perform digital processing of the RF signal,as functionally shown in FIG. 2. FIG. 2 depicts such functional entitiesof the master unit 10 and a remote unit 11 connected via the transportmedium 12 to the master unit 10 that are used in the downlink directionD for processing the RF input signal RF_(IN) for retransmission.

In the embodiment of FIG. 2, the master unit 10 includes a receivingsection 20 for processing an RF input signal RF_(IN) received by theantenna 100. In particular, the receiving section 20 includes an RFfilter 201 in the shape of a bandpass filter for filtering out afrequency band to be processed and transported for retransmission. Fromthe RF filter 201, the RF input signal RF_(IN) is fed to a low noiseamplifier 202 and to a downconverter 203 for downconverting the RFsignal into an intermediate frequency band. After that, the signal isfed to an analog-to-digital converter 204 for digitizing the RF signal,such that an (intermediate-frequency) digital signal IF_(IN) isobtained.

Alternatively, the RF signal may instead be downconverted into abaseband IQ signal (Zero IF).

The digital signal IF_(IN) is fed to a digital signal processing unit(DSP, FPGA, ASIC or the like) 205 and is digitally processed in thedigital signal processing unit 205.

After digital signal processing, the processed signal is, via thetransport medium 12, transported to a digital signal processing unit 206of a transmitting section 21 of a remote unit 11, in which the signal isfurther processed such that a digital signal IF_(OUT) in theintermediate frequency range is obtained. This digital signal IF_(OUT)is converted to an analog RF signal by a digital-to-analog converter207, upconverted by an upconverter 208, power-amplified by a poweramplifier 209, filtered by an RF filter 210 in the shape of a bandpassfilter, and transmitted as an RF output signal RF_(OUT) via the antenna110 of the remote unit 11.

Instead of a single digital-to-analog converter, alternatively twodigital-to-analog converters for the I/Q signal paths and anupconversion using a modulator may be used.

In the uplink direction U, essentially the same processing occurs, wherean RF input signal is received and processed by a receiving section 20of a remote unit 11 and is further processed and transmitted via atransmitting section 21 of the master unit 10.

Digital filtering can occur within the digital signal processing units205, 206. Within the digital signal processing units 205, 206, subbandscontained in the frequency band processed by the repeater system 1 maybe isolated from each other and may be processed separately by digitalfilters. Each digital filter can include a passband associated with acarrier of a communication channel of a communication network, where thedigital filters may be programmable in bandwidth, center frequency, andpassband characteristics.

As indicated in FIG. 1, the train 4 moves forward in a direction oftravel V. This can cause the location of the master unit 10 with itsantenna 100 to change with regard to the base station 3A to which it iscurrently connected (e.g., mobile devices 5 within the train 4communicate via the master unit 10 with the base station 3A). As theantenna 100 moves out of a cell spanned by the base station 3A andenters into a cell spanned by another base station 3B, the mobiledevices 5 communicating via the master unit 10 may trigger a handovercausing a communication connection to be handed over from the (former)base station 3A to the (new) base station 3B. This can occur, asillustrated in FIG. 3, if, for example for an LTE connection, thereference signal receive power (RSRP) of the form a base station 3Adecreases and the reference signal receive power of the new base station3B increases such that a difference between the two exceeds a giventhreshold. Once the difference exceeds the threshold, the handover istriggered and the communication connection is switched over from theformer base station 3A to the new base station 3B.

Although a handover scenario is illustrated in FIG. 3 according to anLTE connection characterized by its reference signal receive power(RSRP), this is not to be understood as limiting. In principle, the sameapplies for connections of other radio access technologies (e.g., GSM,UMTS, or the like), where different measures may be taken to determinethe strength or quality of a received signal.

As in the setup of FIG. 1, communication connections of the mobiledevices 5 located within the train 4 can be routed via the same masterunit 10 and its antenna 100. Handovers of the mobile devices 5 and theircommunication connections can occur at substantially the same time,leading to an increased handover outage probability. As a consequence,calls may be dropped and data connections may be interrupted. If, forexample, hundreds of passengers are riding on a train 4, this may be aproblem.

FIG. 4 illustrates one example of a solution. In this setup, differentrepeater systems having different master units with different antennas100 are installed on the different carriages 40 of a train 4. In thiscase, the antenna 100 can enter into a handover area in between thecells CA, CB of the different base stations 3A, 3B at different times,such that the handovers are split by carriage and do not all occur atthe same time. This may involve increased costs, due to the need toinstall different repeater systems on the different carriages. Further,if a handover of users in a carriage 40 fails, there may be interferencewith handovers of users in a subsequent carriage if the mobile devices 5try to reconnect with the former base station 3A.

FIG. 5 depicts a setup that can overcome at least some of these issues.In this setup, two master units 10 ₁, 10 ₂ are installed on the train 4:a first master unit 10 ₁ is installed on a first carriage 40 and asecond master unit 10 ₂ is installed on a rear carriage 40 of the train4 (referring to the direction of travel V). Each master unit 10 ₁, 10 ₂can be directly connected to an antenna 100 ₁, 100 ₂ (for example by acoaxial cable) via which it may exchange signals with base stations 3A,3B outside of the train 4. In addition, each master unit 10 ₁, 10 ₂ canbe connected to multiple remote units 11 ₁-11 _(X). At least one remoteunit 11 ₁-11 _(X) can be installed on each carriage 40.

Each of the remote units 11 ₁-11 _(X) is connected to both master units10 ₁, 10 ₂ via a transport medium 12, for example a ring bus connectionor the like. In addition, each of the remote units 11 ₁-11 _(X) isconnected to an antenna system 110 ₁-110 _(X) for transmitting RFsignals into the associated carriage 40 and to receive RF signals out ofthe carriage 40. The antenna system 110 ₁-110 _(X) may be a leaky feederor another suitable antenna for providing coverage within a carriage 40.

A mobile device 5 within a carriage 40 can communicate via the remoteunit 11 ₁-11 _(X) of the associated carriage 40 and one or both masterunits 10 ₁, 10 ₂ with an outside base station 3A. The connection withthe first master unit 10 ₁ may have a first gain and the connection withthe second master unit 10 ₂ may have a second gain. The gain settingscan be controlled via a control unit 13 that may be a separate unitlocated somewhere on the train 4 or that may be integrated into one ofthe master units 10 ₁, 10 ₂.

By the gain settings it can be prioritized via which master unit 10 ₁,10 ₂ a mobile device 5 within a particular carriage 40 communicates withan outside base station 3A, 3B. This may in particular be used tocontrol a handover of mobile devices 5 within the different carriages 40of the train 4.

For example, when looking at the second remote unit 11 ₂, by suitablyadjusting the gain setting of the connection of the remote unit 11 ₂with the first master unit 10 ₁ and the gain setting of the connectionwith the second master unit 10 ₂, a mobile device 5 within the carriage40 associated with the second remote unit 11 ₂ can be forced to handoverfrom the former base station 3A to the new base station 3B. Byincreasing the gain of the connection between the remote unit 11 ₂ andthe first master unit 10 ₁ and by at the same time decreasing the gainof the connection between the remote unit 11 ₂ and the second masterunit 102, the signals adopted by the antenna 100 ₁ of the first masterunit 10 ₁ can be prioritized. Because the antenna 100 ₁ of the firstmaster unit 10 ₁ is already in the handover area HO and in the range ofthe new base station 3B, the mobile devices 5 within the coverage areaof the remote unit 11 ₂ can be forced to handover to the new basestation 3B.

The same may occur for the next, consecutive remote unit 11 ₃ with anappropriate time offset, such that the mobile devices 5 in the coveragearea of the next remote unit 11 ₃ perform their handover in atime-offset manner with respect to the mobile devices 5 in a carriage 40associated with the previous remote unit 11 ₂.

By applying the individual gain adjustment in a consecutive manner, thewhole handover scenario of the train 4 can be controlled such that thehandovers of the mobile devices 5 within the train 4 do not occur at thesame time, but in a time offset manner. By dynamically adjusting thegain settings of the connections of the remote units 11 ₁-11 _(X), thehandover scenarios can be flexibly influenced to force the mobiledevices 5 to perform their handovers at suitable times in a staggeredmanner.

Controlling the gain setting by the control unit 13 may depend on areference signal power level measured at the first master unit 10 ₁ andthe second master unit 10 ₂. Alternatively, location information, forexample obtained via a GPS system, may be used, making use of theknowledge that at a certain location the cell of a certain base station3A, 3B is entered or left.

A flow chart of an example of a process for controlling the gainsettings of the connections of the remote units 11 ₁-11 _(X) isillustrated in FIG. 6. In block S1 it is checked whether a handover areaHO is approached. If this is not the case, normal operation iscontinued, while also continuing checking whether a handover area isapproached in block S2.

If it is found that a handover area HO is approached in block S1, forexample by measuring a reference signal power level at the master units10 ₁, 10 ₂, in block S3 the gain between the first master unit 10 ₁ andthe remote units 11 ₁-11 _(X) may be reduced to avoid a prematurehandover of the mobile devices 5 on the train 4.

In block S4 it is checked whether a handover condition is fulfilled atthe first master unit 10 ₁. If this is the case, it is moved to blockS5. If this is not the case, block S4 is repeated.

If the handover condition is fulfilled at the master unit 10 ₁, firstthe gain of the connection between the first master unit 10 ₁ and thefirst remote unit 11 ₁ can be increased and, at the same time, the gainbetween the second master unit 10 ₂ and the first remote unit 11 ₁ canbe decreased. It can be checked whether for the mobile devices 5connected to the first remote unit 11 ₁ the handover procedures havebeen successful. If not, it is waited for a guard period and thenchecked again in block S7. If the handover procedures have beensuccessful, the gain between the first master unit 10 ₁ and the secondremote unit 11 ₂ is increased and at the same time the gain between thesecond master unit 10 ₂ and the second remote unit 11 ₂ is decreased toforce the mobile devices 5 associated with the second remote unit 11 ₂into a handover. It then is checked whether the handovers for the mobiledevices 5 associated with the second remote unit 11 ₂ have beensuccessful in block S9.

The blocks can be repeated for further remote units 11 ₃-11 _(X) untilthe handovers for the mobile devices 5 associated with the remote units11 ₁-11 _(X) occur, in blocks S11, S12, S13.

In some examples, it can be possible to split the number of mobiledevices starting a handover scenario into several smaller handovers(e.g., decrease the handover outage probability). The handover cycle ofthe individual carriages can be artificially stretched in case of ahandover outage of one of the other carriages. A handover area can beshifted (e.g., by moving the handover area to regions with low drivingspeed to increase the handover success probability). The handoverprocess of the whole train can be linked to GPS data available in theDAS (e.g., once the trains front antenna enters a specific GPS location,the handover scenario will be started). The handover process can betriggered by measuring the reference signal power level at the firstmaster unit and the second master unit. In other examples, additionalfeatures can be realized by the end user.

In some examples, assuming the train is moving in an area where nohandover is to be performed, the two roof antennas may be used for 2×2MIMO (Multiple Input Multiple Output) transmissions. For example, theantenna network inside the train can be doubled. Once a handover isexpected, the MIMO operation can be switched to common SISO (SingleInput Single Output) operation to control the handover in the same wayas discussed above.

The foregoing description of certain examples, including illustratedexamples, has been presented only for the purpose of illustration anddescription and is not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed. Numerous modifications,adaptations, and uses thereof will be apparent to those skilled in theart without departing from the scope of the disclosure.

What is claimed is:
 1. A repeater system comprising: a first master unit positionable at a first location on a movable object and a second master unit positionable at a second location on the movable object, the first master unit and the second master unit being configured to communicatively couple to antennas for receiving a downlink RF signal from at least one base station external to the movable object and for transmitting an uplink RF signal towards the at least one base station; and remote units configured to couple through a transport medium to the first master unit by a first connection and to the second master unit by a second connection, the remote units being positionable on the movable object and associated with different coverage areas within the movable object, the remote units being configured to couple to antenna systems for transmitting the downlink RF signal into associated coverage areas of the movable object and for receiving the uplink RF signal from the coverage areas, wherein, for at least a subgroup of the remote units, a first gain for the first connection and a second gain for the second connection are controllable by a control unit.
 2. The repeater system according to claim 1, further comprising the control unit configured to increase or decrease the first gain for the first connection with the first master unit and the second gain for the second connection with the second master unit.
 3. The repeater system according to claim 2, wherein the control unit is configured to increase the first gain based on decreasing the second gain and to decrease the first gain based on increasing the second gain.
 4. The repeater system according to claim 2, wherein the control unit is configured to adjust the first gain and the second gain for different remote units such that the first gain and the second gain of the remote units associated with neighbouring coverage areas are adjusted consecutively.
 5. The repeater system according to claim 2, wherein the control unit is configured to control the first gain or the second gain for a particular remote unit to trigger a handover of a mobile device operating in a coverage area associated with the particular remote unit, from a first base station spanning a first communication cell to a second base station spanning a second communication cell, wherein at least one of the first master unit or the second master unit is located in the range of each communication cell.
 6. The repeater system according to claim 2, wherein the control unit is configured to control the first gain and the second gain based on a signal strength measurement of a signal received from a base station or location information received from a positioning system.
 7. The repeater system according to claim 1, wherein the first gain and the second gain are individually adjustable for each of the remote units.
 8. The repeater system according to claim 1, wherein the movable object is a train.
 9. The repeater system according to claim 8, wherein the first master unit is positionable proximate to a first end of the train and the second master unit is positionable proximate to a second end of the train that is an opposite end to the first end.
 10. The repeater system of claim 9, wherein the train comprises a plurality of train cars, wherein the remote units are positionable in the plurality of train cars such that each train car includes a remote unit.
 11. A method comprising: receiving, by a first master unit at a first location on a movable object and a second master unit located at a second location on the movable object, a downlink RF signal from at least one base station that is located outside of the movable object; transmitting, by remote units associated with different coverage areas within the movable object and connected to the first master unit and the second master unit via a transport medium, the downlink RF signal into an associated coverage area of the movable object; receiving, by the remote units, an uplink RF signal from a coverage area; transmitting, by the first master unit and the second master unit, the uplink RF signal towards the at least one base station; and controlling, for at least a subgroup of the remote units by a control unit, a first gain for a connection with the first master unit and a second gain for the connection with the second master unit.
 12. The method according to claim 11, further comprising: increasing the first gain in response to decreasing the second gain.
 13. The method according to claim 11, decreasing the first gain in response to increasing the second gain.
 14. The method according to claim 11, wherein controlling the first gain and the second gain includes adjusting the first gain and the second gain for different remote units such that the first gain and the second gain of the remote units associated with neighbouring coverage areas are adjusted consecutively.
 15. The method according to claim 11, wherein controlling the first gain and the second gain includes controlling the first gain or the second gain for a particular remote unit to trigger a handover of a mobile device operating in the coverage area associated with the particular remote unit, from a first base station spanning a first communication cell to a second base station spanning a second communication cell, wherein at least one of the first master unit or the second master unit is located in the range of each communication cell.
 16. The method according to claim 11, wherein controlling the first gain and the second gain includes controlling the first gain and the second gain based on a signal strength measurement of a signal received from a base station or location information received from a positioning system.
 17. The method according to claim 11, wherein controlling the first gain and the second gain includes individually adjusting the first gain and the second gain for each of the remote units.
 18. The method according to claim 11, wherein the movable object is a train.
 19. The method according to claim 18, wherein the first master unit is proximate to a first end of the train and the second master unit is proximate to a second end of the train that is an opposite end to the first end.
 20. The method of claim 19, wherein the train comprises a plurality of train cars, wherein the remote units are in the plurality of train cars such that each train car includes a remote unit. 